1. Field of the Invention
The present invention relates to an obstacle detector for a vehicle.
2. Description of the Related Art
Devices for detecting obstacles surrounding a vehicle have been in practical use today. The obstacle detectors for a vehicle may be divided broadly into two kinds, i.e., the detector utilizing a radar principle to detect the obstacles, and the detector utilizing cameras to detect the obstacles.
Usually, the obstacle detector for a vehicle utilizing the radar principle includes the following types, namely, lazar radar which transmits radar light and detects a position of an obstacle according to the arrival time of the lazar light reflected by the obstacle (for reference, see JP-H05-119147 A), millimeter-wave radar which transmits millimeter-wave in the GHz band and detects a position of an obstacle based on the arrival time of the millimeter-wave reflected by the obstacle (for reference, see JP-H05-273339 A), and supersonic sonar which transmits supersonic and detects a position of an obstacle based on the arrival time of the supersonic reflected by the obstacle (for reference, see JP-H05-210800 A), etc.
Additionally, the obstacle detector for a vehicle utilizing cameras usually includes the following, i.e., a device which detects an obstacle based on differences of images between two successive image-frames of a camera photographing a rear of the vehicle, and a stereo camera device which photographs the front of the vehicle with two cameras and detects an obstacle based on differences between a right image and a left image (for reference, see JP-2004-104478 A).
However, since the lazar radar includes a drive mechanism for scanning the lazar, and the millimeter-wave lazar includes a transmitting and receiving antenna, it is difficult to miniaturize each of them. In addition, they are highly expensive.
Further, although the supersonic is inexpensive, its resolution in the lateral direction is low and may only detect whether there is an object or not, therefore, it is unsuitable for recognizing the position and direction of the obstacle.
Additionally, if the device which detects the obstacle according to the differences of the images between the image-frames of the camera image is used, when the vehicle runs at a low speed, there is nearly no difference in images between the two successive image-frames, so there is a problem that the detection accuracy decreases.
Moreover, in the stereo camera device, there is a problem that the calculation accuracy of the differences between the right and left images gets worse, due to distortion of the lens of the camera, and the detection accuracy of the obstacle decreases. In addition, when the devices are attached to the vehicle, it is necessary to adjust the attachment for every vehicle with high accuracy, so that a large amount of labor is required.
Therefore, at least one object of the present invention is to provide an obstacle detector with high detection accuracy. The obstacle detector detects the obstacle based on the images converted into overhead images of the vehicle surroundings, and divides the area in the vehicle surroundings where the obstacle is to be detected into a plurality of regions, and utilizes properly a plurality of obstacle detection methods in accordance with the divided regions and running status of the vehicle, to improve the obstacle detection accuracy.